Fatty emulsions composed of emulsion particles whose mean particle size is 10-100 nm are known to have effects such as improvement of distribution of drugs through the blood and movement thereof from their sites of application to the lesion tissues, and thus have excellent characteristics which have been hitherto unknown (Japanese Patent Application Disclosure HEI-2-203 etc.).
Generally, it is convenient for fatty emulsions to be preserved in a form readily preparable into emulsions just before their use.
Considering the possibility that the particle size of fatty emulsions changes with time, said fatty emulsions are preferred to be lyophilized preparations.
Also drugs in fatty emulsions are easily expected to be stable at low temperatures and in a dry state, which is an additional reason for the preference of lyophilized preparations.
Studies have long been made regarding techniques for lyophilization of emulsions. For example, liposomes different from the fatty emulsions of the present invention are disclosed in PCT Transfer Japanese Patent Application Disclosure SHO 62-501631, etc., while lyophilized preparations composed of oil in water types of emulsions are disclosed in Japanese Patent Application Disclosure SHO 60-224617, Japanese Patent Application Disclosure SHO 60-239417, etc., respectively. Lyophilization techniques for fatty emulsions with a particle size of 0.2 .mu.m were studied from various points of view, and a remarkable increase in particle size was observed upon redissolution after drying. Moreover, addition of a surfactant, though its clinical safety has not been guaranteed, was tried, with no satisfactory effects.
Fatty emulsions are assembly of low molecular weight compounds in water, and their lyophilization while maintaining the assemby structure was difficult,
We the present inventors have investigated lyophilized preparations of fatty emulsions made of emulsion particles having an mean particle size of 10 nm-100 nm, but this has resulted in major problems in such lyophilized preparations, e.g., the dried cakes are not uniform, are pasty or adhesive, and suffer from cracks, cut-outs, shrinkage and so on. Additional serious defects were that an increase in particle size was observed after redissolution and many emulsion particles that exceeded 100 nm in particle size were found.
For the production of lyophilized preparations of fatty emulsions, generally, the use of an aid has been attempted for lyophilization. Such an aid includes a monosaccharide such as glucose, a disaccharide such as trehalose, other saccharides such as sorbitol, starch, etc., an amino acid such as glycine, dextran, glycol or a derivative thereof (for example, Japanese Patent Application Disclosure SHO 62-29513).
Even with the use of these aids, however, lyophilized preparations of fatty emulsions composed of emulsion particles, which maintained the mean particle size of 10 nm-100 nm or the value observed prior to the lyophilization, could not be obtained.